Protovis is an open-source visualization library by the Stanford Visualization Group and has become one of the preferred tools in our arsenal. If you want to get started with the popular toolkit too, Jerome Cukier has a comprehensive tutorial about how to work with data in Protovis.
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The New York Times has been busy publishing their news vocabulary as linked open data since 2009. Now, Evan Sandhaus has published a short but thorough tutorial about building an application that's based on this data.
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